Shock absorbing device



y 1955 A. s. FLETCHER ET AL 2,713,466

SHOCK ABSORBING DEVICE Filed Jan. 25, 1950 2 Sheets-Sheet lBE/777E/V/4L/"7M GEORGES/VIVA L,

F. 3 a/wv/cz PERM/v5,

'9 Attorney July 19, 1955 A, s. FLETCHER ET AL 2,713,466

SHOCK ABSORBING DEVICE Filed Jan. 25, 1950 2 Sheets-Sheet 2 Fiq. 5 Fig.7

BERT/E IV/LL/FM GEORGE SIVVILL,

2 ikg l Attorney United States Patent C 2,713,466 SHOCK ABSORBING DEVICEAlexander Spurgeon Fletcher, Farnborough, Bertie William George Savill,Frimley, and Daniel Perkins, Bedford, England, assignors to the Ministerof Supply, in His Majestys Government of the United Kingdom of GreatBritain and Northern Ireland, London, England Application January 25,1950, Serial No. 140,368

Claims priority, application Great Britain January 31, 1949 17 Claims.(Cl. 244-138) This invention relates to shock-absorbing devices and ismore especially, though not exclusively, concerned with such devices foruse with parachute-borne and other objects dropped from aircraft.

In connection with shock-absorbing landing gear for parachute-borneobjects, we have carried out experiments with air-filled bags providedwith holes through which the air escaped as it was compressed under themomentum and weight of the object, giving a dash-pot type ofshock-absorption. In order to prevent eventual bursting of the bags andconsequent loss of cushioning effect just when most required, it wasnecessary to use holes of such size that air escaped freely in the earlystages of collapse of the bags. The object of the present invention isto provide shock-absorbing devices giving more satisfactory cushioningand a feature of it is the covering of a hole or holes in a pneumaticshock-absorbing bag with a membrane or membranes which is or are ofmaterial which is more expansible than the material of which the bagitself is made and/ or which will fracture at a much lower strain thanwill such latter material. The use of the membrane pr longs theretention of the original volume of air and ensures an initialcompression thereof before relatively freeor even full-bore escapethrough the hole or holes in the bag proper is permitted.

In our previous experiments, the filling of the bags during free fallwas by way of the laterally disposed escape holes: this resulted inincomplete inflation of the bags and a reduced working volume of air. Wenow prefer, as a further feature of our invention, to employ holes inthe bottom of the bags, whereby forced inflation is effected duringdescent, escape of air through the filling holes during compressionunder load being prevented by non-return valves.

The above and other features of the invention are embodied in theparachute-borne load-support and landing gear therefor which isillustrated bythe drawings: in which:

Figure 1 is an end view of part of the support and landing gear, thebags of the latter being in deflated condition,

Figure 2 is a similar view, to an enlarged scale, the bags being showninflated,

Figure 3 is a side view, the parts being shown in the same condition asin Figure 2,

Figure 4 is a section through the base-board and the lower portion ofone bag of the landing gear,

Figure 5 is a sectional view through a portion of a bag to illustrate adetail,

Figure 6 is a view similar to that of Figure 5 illuslustrated is afreight container 10 and the landing gear lot:

therefor comprises three inflatable bags 11, 12 and 13 of multi-plyrubberised fabric suspended from the underside of the floor of thecontainer and carrying a base-board 14 of plywood. The suspension ofeach bag is effected by means of cords 15 of suitable breaking strainpassed through eyelets 16 in the rubberised fabric and through eyebolts(not shown) in the container floor; a similar form of attachment isemployed between each bag and the base-board, the relevant cords beingindicated at 17.

Each bag is of substantially oblate spheroid shape when inflated and thebags are reinforced with endless flexible wire grommets 18. A number ofcircular holes 19 are formed in the side wall of each bag, in theneighbourhood of the equator thereof and so positioned as not to bemasked by an adjacent bag. These holes are covered by thin membranes 20of rubber or other suitable expansible material cemented to the insideof the bags walls. A circular hole 21 is formed centrally in the bottomof each bag and registering holes 22 are provided in the base-board; thepassage of air through these holes is controlled by simple non-returnvalves each comprising a disc 23 of fabric of greater diameter than theassociated hole, anchored inside the bag by elastic cords 24 to lieconcentric with the hole. The alignment of the holes in the bags withthe corresponding holes in the base-board is ensured by means of annularplywood frames 25 (see Figure 4) cemented to the outside of the bagsconcentric with the holes therein and normally retained within thecorresponding holes in the base-board by means of spring-pressed ballcatches 26.

The landing gear is completed by door members 27, 28 hinged to fairings29, 30 carried by the container at each side thereof. These door membersare normally locked together, by means of releasable locking means 31,32 in the position indicated by Figure 1 in which they contact thebase-board and retain the bags in deflated, folded condition against theunderside of the container floor. Elastic cords 33, anchored to thecontainer are attached to wire cables 34, which pass over pulleys 35 andare anchored to the respective door members: the elastic cords 33 arenormally stretched and serve to cause the door members 27, 28 whenreleased by the locking means 31, 32, to open outwardly to the positionsshown in Figure 2, where they abut against the respective fairings andare inclined slightly upwards.

Upon the container being dropped from the transporting aircraft todescend under the retarding influence of parachute equipment attached bymeans of lines (of which two are shown at 36 and 37 in Figure 2), delaymechanism (not illustrated) is set in operation which releases the doormembers after a predetermined interval. The opening of the door members,by means of the elastic cords, releases the base-board which drops toextend the bags; the non-return valves 23, 24 are opened by the dynamicpressure due to the passage of the equipment through the air, whichpressure also results in rapid and complete inflation of the bags.

When the base-board strikes the ground, the non-return valves preventescape of air through the filling holes and the air within the bagsbecomes compressed, the thin membranes 2% being forced to expand throughthe holes in the bag to form small balloons; when a sufiicient internalpressure is reached, the membranes burst and the absorption of shock isthereafter achieved by the dash-pot effect of the air escaping throughthe holes in the bags.

Horizontal velocity of the container relatively to the ground and/or thebase-board is accommodated by a rolling action in the deflating bags andthe effect of this action in preventing damage to the container andcontents is augmented by the use of cord of suitable breaking strain forthe securing of the air bags to the container and to the base-board; ifand when, the attachment cords break, the ball catches 26 associatedwith the plywood frames 25 offer very little resistance to completedetachment of the bags from the base-board. The function of the doormembers, when in the opened condition, is to give stability againstoverturning of the container, particularly if dragged along the groundby a parachute which has not been freed on touch-down.

In the modification illustrated by Figure 6, small holes 41 are providedin the membranes 2!); ,in operation these holes become enlarged as thematerial of the membranes expands under the internal air pressure,providing gradually increasing exit paths for the air. The arrangementmay be such that the membranes eventually burst (as in the previouslydescribed arrangement) or that the holes therein become suflicientlylarge to provide the required escape path for air.

In the modification illustrated by Figure 7, the single membranes soprovided to cover each hole I19 in the arrangements according to Figure5 or 6 are replaced by pairs of membranes 38 and 39 of which eachmembrane 38 is apertured, as at 4% and is of material more easilyfrangible than the material of which the bag is made; each membrane 39covers the aperture 40 in the associated membrane 38 and is of materialwhich is more easily frangible than that of which the membranes 38 aremade. Normally, the action will be similar to that previously describedthe membranes 39 above being fractured in the shock-absorbing action.Should the container land at an unduly high speed, however (for example,due to a parachute failure), fracture of the membranes 39 will bequickly followed by fracture of the membranes 38 to provide enlargedair-escape holes with a view to preventing bursting of the bags andconsequent complete loss of shock-absorbing effect.

We claim:

1. A pneumatic shock-absorbing device comprising an inflatable,perforated bag and a membrane covering a perforation in said bag and oflower breaking strain than said bag, whereby said bag will absorb arelatively violent initial impact Without bursting, but will stillretain suflicient air to afford continued cushioning after the initialimpact.

2. A pneumatic shock-absorbing device comprising an inflatable,perforated bag and a membrane covering a perforation in said bag and ofelastic material which is more expansible than the material of whichsaid bag is made, whereby said bag will absorb a relatively violentinitial impact without bursting, but will still retain sufficient air toafford continued cushioning after the initial impact.

3. A pneumatic shock-absorbing device comprising an inflatable,perforated bag and a perforated membrane covering a perforation in saidbag and of material which is more expansible than that of which said bagis made, whereby said bag will absorb a relatively violent initialimpact without bursting, but will still retain sufficient air to affordcontinued cushioning after the initial impact.

4. A pneumatic shock-absorbing device comprising an inflatable,perforated bag, an apertured membrane covering a perforation in said bagand of lower breaking strain than said bag and a second membranecovering the aperture in said apertured membrane and of lower breakingstrain than said apertured membrane, whereby said bag will absorb arelatively violent initial impact without bursting, but will stillretain suflicient air to afford continued cushioning after the initialimpact.

5. A pneumatic shock-absorbing device comprising an inflatable,perforated bag of rubberized fabric and membranes of rubber coveringperforations in said bag whereby said rubber membranes will permit saidbag to absorb will retain sufficient air to afford continued cushioningafter'the initial impact.

6. Pneumatic shock-absorbing means for cushioning the alighting of anobject dropped from the air comprising a perforated bag, a membrane ofrelatively easily frangible material covering a perforation in said bagand non-return valve means in the bottom of said bag whereby said bagmay be inflated by the air pressure developed during the dropping of theobject.

7. A support for a load to be dropped from the air provided withshock-absorbing alighting gear comprising an inflatable, perforated bag,a membrane covering a perforation in said bag and of lower breakingstrain than said bag, a base-board attached to said bag and means forreleasably securing said base-board to said support in a relation suchthat said bag is retained in a deflated condition.

8. A load-support as claimed in claim 7 in which the means forreleasably securing said base-board comprises a pair of members hingedto said load-support, spring means urging said hinged members to swingclear of said base-board and locking means for releasably holding saidhinged members against the action of said spring means.

9. A load-support as claimed in claim 8 in which said hinged members arehinged on axes substantially parallel to the normal direction ofhorizontal motion of the load-support and are arranged, under the actionof said spring means, to take up positions in which their under surfacesare upwardly inclined in relation to the loadsupport.

10. A support for a load to be dropped from the air havingshock-absorbing alighting gear comprising a plurality of perforated,inflatable bags, membranes covering perforations in said bags and moreeasily frangible than said bags, a base-board and cords of lowerbreaking strain than the material of said bags securing said bags tosaid base-board.

11. A support for a load to be dropped from the air having shockabsorbing alighting gear comprising an inflatable, perforated bag, amembrane of relatively elastic material covering a perforation in saidbag, a base-board, and cords securing said bag to said load-support andto said base-board and of breaking strain less than that of the materialof which said bag is made.

12. A support for a load to be dropped from the air havingshock-absorbing alighting gear comprising an inflatable, perforated bag,a relatively easily frangible membrane covering a perforation in saidbag, an apertured base-board, non-return valve means whereby said bagmay be inflated by way of the aperture in said base-board, cords ofrelatively low breaking strain securing said bag to said load-supportand to said base-board, an apertured member secured to said bag andspring-pressed locking means for releasably securing said member withits aperture coaxial with that of said base-board.

13. A support for a load to be dropped from the air havingshock-absorbing alighting gear comprising a plurality of perforated,inflatable bags, an apertured baseboard, cords of relativelylow-breaking strain securing said bags to said load-support and to saidbase-board so that the perforations of one bag are not masked by anotherbag when in the inflated condition, membranes of relative- 1y easilyfrangible material covering perforations in said bags and non-returnvalve means whereby said bags may be inflated by way of apertures insaid base-board.

14. A support for a load to be dropped from the air havingshock-absorbing alighting gear comprising a plurality of perforated,inflatable bags, membranes of relatively expansible elastic materialcovering perforations in said bags, a base-board secured to said bags,hinged members carried by the load-support, releasable locking means forholding said hinged members in positions such that they contact saidbase-board and thereby retain said bags a relatively violent initialimpact without bursting, but I in deflated condition and elastic cordsadapted, upon release of said hinged members, to pull then: clear ofsaid base-board.

15. A load-support as claimed in claim 14 in Which said elastic cordsare anchored to the load-support and are secured to relativelynon-extensible cords anchored to said hinged members.

16. A parachute-borne load-support having shock-abs Jrbing alightinggear comprising a plurality of perforated bags or substantiallyoblate-spheroid shape, cords securing the upper portions of said bags tosaid load-support, membranes covering perforatiens in said bags and moreexpansible and more easily frangible than said bags, an aperturedbase-board, cords securing said baseboard to the lower portions of saidbags, non-return valve means whereby said bags may be inflated by way ofthe apertures in said base-board, hinged members carried by saidload-support, releasable locking-means adapted to retain said hingedmembers in contact with said base-board and thereby to retain said bagsin deflated condition and spring means, carried by said load-support,adapted 0 cause said hinged members, when released by said lockingmeans, to

6 swing clear of said baseboard to allow it to fall in relation to saidlead-support.

17. A support fer a load to be dropped from the air havingshock-abserbing alighting gear comprising an inflatable, perforated bag,membranes covering perforations in bag and mere easily frangible thansaid bag, a baseboard carried by said bag and having an aperturetherein, said bag having an opening aligned with said aperture to permitair to enter and inflate said bag, and non-return valve means associatedWith said aperture preventing egress of air from the bag through theaperture in said baseboard.

References Gated in the file of this patent UNITED STATES PATENTS

